This invention relates to fluid-gauging probes.
Ultrasonic fluid-gauging probes, such as for measuring the height of fuel in an aircraft fuel tank, are now well established and examples of systems employing such probes can be seen in U.S. Pat. No. 5,670,710, GB2380795, GB2379744, GB2376073, U.S. Pat. No. 6,598,473 and U.S. Pat. No. 6,332,358. The probe usually has a tube or still well extending vertically in the fuel tank and a piezoelectric ultrasonic transducer mounted at its lower end. When the transducer is electrically energized it generates a burst of ultrasonic energy and transmits this up the still well, through the fuel, until it meets the fuel surface. A part of the burst of energy is then reflected down back to the same transducer. By measuring the time between transmission of the burst of energy and reception of its reflection, the height of fuel in the still well can be calculated.
Because the probe only has one transducer, failure or partial failure of the transducer or its associated electrodes or electrical circuit results in a complete loss of information from the probe. In order to provide sufficient reliability and redundancy in, for example, aircraft applications, it is usual to provide additional probes so that sufficient information can be provided in the event of probe failure. This leads to extra cost and weight.